Nyob rau hauv cov noob caj noob ces, cov txheej txheem ntawm DNA, RNA thiab protein synthesis muab faib ua peb theem kom yooj yim ntawm kev piav qhia: pib, elongation thiab txiav. Cov theem no piav qhia txog cov txheej txheem sib txawv rau cov khoom sib txawv ntawm cov molecules, txawm li cas los xij, lawv ib txwm txhais tau tias qhov pib, qhov kawg ntawm cov txheej txheem, thiab qhov kawg. Replication termination yog qhov kawg ntawm kev sib txuas ntawm DNA molecules.
Lub luag haujlwm lom ntawm kev txiav tawm
Kev pib thiab txiav tawm yog thawj zaug thiab zaum kawg ciam teb ntawm kev loj hlob ntawm cov saw hlau sib txuas, uas yog ua tiav ntawm theem elongation. Kev ua tiav ntawm cov txheej txheem feem ntau tshwm sim qhov twg cov khoom siv roj ntsha ntawm kev sib txuas ntxiv xaus (piv txwv li, ntawm qhov chaw ntawm qhov kawg ntawm qhov rov ua dua lossis cov ntawv sau). Tib lub sijhawm, kev txiav tawm ua 2 lub luag haujlwm tseem ceeb:
- tsis tso cai rau kev sib txuas mus dhau ib ntu tshwj xeeb ntawm cov saw matrix;
- tso tawm cov khoom siv biosynthetic.
Yog li, piv txwv li, hauv cov txheej txheem ntawm kev sau ntawv (synthesis ntawm RNA raws li DNA qauv), kev txiav tsis pub cov txheej txheem hla ciam teb ntawm ib qho gene lossis operon. ATtxwv tsis pub, cov ntsiab lus semantic ntawm tus xa xov RNA yuav raug ua txhaum. Nyob rau hauv rooj plaub ntawm DNA synthesis, kev txiav tawm ua rau cov txheej txheem nyob rau hauv ib tug replican.
Yog li, kev txiav tawm yog ib qho ntawm cov txheej txheem tswj kev sib cais thiab kev ua kom zoo ntawm biosynthesis ntawm ntau ntu ntawm matrix molecules. Tsis tas li ntawd, qhov kev tso tawm ntawm cov khoom tso cai rau tom kawg ua nws txoj haujlwm, thiab tseem rov qab cov txheej txheem rau nws lub xeev qub (detachment of enzyme complexes, restoration of the spatial structure of the matrix, etc.).
Dab tsi yog qhov txiav tawm ntawm DNA synthesis
DNA synthesis tshwm sim thaum rov ua dua, txheej txheem ntawm ob npaug ntawm cov khoom siv caj ces hauv ib lub xovtooj. Nyob rau hauv cov ntaub ntawv no, tus thawj DNA unwinds, thiab txhua ntawm nws chains ua hauj lwm raws li ib tug template rau ib tug tshiab (tus ntxhais) ib tug. Raws li qhov tshwm sim, ob qho tag nrho DNA molecules tau tsim nyob rau hauv qhov chaw ntawm ib ob-stranded helix. Kev txiav tawm (kawg) ntawm cov txheej txheem no hauv prokaryotes thiab eukaryotes tshwm sim txawv vim qee qhov sib txawv ntawm cov txheej txheem ntawm chromosome replication thiab nucleoid ntawm cov hlwb tsis muaj nuclear.
How replication ua haujlwm
Tag nrho cov proteins uas tau koom nrog hauv kev rov ua dua. Lub luag haujlwm tseem ceeb yog ua los ntawm synthesis enzyme, DNA polymerase, uas ua rau kev tsim cov phosphodiester bonds ntawm nucleotides ntawm cov saw loj hlob (tom kawg raug xaiv raws li lub hauv paus ntsiab lus ntawm complementarity). Txhawm rau pib ua haujlwm, DNA polymerase yuav tsum muaj primer - primer uas yog tsim los ntawm DNA primase.
Qhov kev tshwm sim no yog ua ntej los ntawm kev tshem tawm DNA thiab kev sib cais ntawm nws cov saw hlau,txhua yam uas ua hauj lwm raws li ib tug matrix rau synthesis. Txij li thaum tom kawg tuaj yeem tshwm sim los ntawm 5 'mus rau 3' kawg, ib qho strand dhau los ua tus thawj coj (kev sib txuas ua haujlwm nyob rau pem hauv ntej thiab tsis tu ncua), thiab lwm yam strand ua lagging qab (tus txheej txheem yog ua nyob rau hauv lub opposite direction thiab fragmentarily.). Qhov sib txawv ntawm cov khoom tawg yog tom qab kho los ntawm DNA ligase.
Lub unwinding ntawm ob lub helix yog ua los ntawm DNA helicase enzyme. Cov txheej txheem no tsim cov qauv Y-shaped hu ua replication diav rawg. Qhov tshwm sim ib leeg-stranded cheeb tsam yog ruaj khov los ntawm lub npe hu ua SSB proteins.
Termination yog qhov nres ntawm DNA synthesis, uas tshwm sim los ntawm lub rooj sib tham ntawm replication forks, los yog thaum kawg ntawm chromosome mus txog.
Txoj kev txiav tawm hauv prokaryotes
Kev ua tiav ntawm kev rov ua dua hauv prokaryotes tshwm sim ntawm qhov tsim nyog hauv genome (qhov chaw txiav tawm) thiab txiav txim siab los ntawm ob yam:
- replication fork meeting;
- ter-sites.
Lub rooj sib tham ntawm rab diav rawg tshwm sim yog tias DNA molecule muaj lub voj voog kaw, uas yog tus yam ntxwv ntawm feem ntau prokaryotes. Raws li qhov tshwm sim ntawm kev sib txuas txuas ntxiv, 3' thiab 5' kawg ntawm txhua txoj saw txuas txuas. Rau unidirectional replication, qhov match point yog tib yam li lub hauv paus chaw (OriC). Nyob rau hauv cov ntaub ntawv no, lub synthesized saw, raws li nws yog, mus nyob ib ncig ntawm lub nplhaib molecule, rov qab mus rau qhov chaw pib thiab ntsib nrog 5'-kawg ntawm nws tus kheej. Nrog bidirectional replication (synthesis tshwm sim ib txhij nyob rau hauv ob qho kev qhia los ntawm OriC point), lub rooj sib thamdiav rawg thiab kev sib txuas ntawm qhov kawg tshwm sim nyob rau hauv nruab nrab ntawm lub nplhaib molecule.
Kev sib txuas ntawm cov nplhaib yog ua los ntawm DNA ligase. Qhov no tsim ib qho qauv hu ua cathekan. Los ntawm kev qhia txog ib qho kev sib tsoo, DNA gyrase rhuav tshem cov nplhaib thiab cov txheej txheem rov ua kom tiav.
Ter-sites kuj koom nrog hauv kev rov ua dua. Lawv nyob 100 lub hauv paus khub dhau ntawm qhov chaw uas cov diav rawg sib ntsib. Cov cheeb tsam no muaj ib ntus luv luv (23 bp) uas cov khoom lag luam protein ntawm tus noob khi, thaiv qhov kev nce qib ntxiv ntawm kev rov ua dua tshiab.
Kev rov ua dua tshiab hauv eukaryotic cell
Thiab lub sijhawm kawg. Hauv eukaryotes, ib chromosome muaj ob peb lub ntsiab lus ntawm kev pib rov ua dua, thiab kev txiav tawm tau tshwm sim hauv ob qhov xwm txheej:
- thaum diav rawg txav mus rau sab nraud kev sib tsoo;
- yog tias qhov kawg ntawm chromosome mus txog.
Thaum kawg ntawm cov txheej txheem, cov DNA molecules sib cais khi rau chromosomal proteins thiab tau muab faib rau hauv cov ntxhais cell.
